Current switching device for electromagnetic hammers



June 23, 1959 w. F. PRAEG 2,892,140

CURRENT SWITCHING DEVICE FORv ELECTROMAGNETIC HAMMERS Filed Aug. 30. 1956 2 Sheets-Sheet l INVENTOR. Wfl/.TEE ,0F/156 fywwufffm A free/vim' June 23, 1959 w. F. PRAEG CURRENT swncHmG DEVICE FOR ELECTEOMAGNETIC HAMMERS 2 Sheets-Sheet 2 'Filed Aug. so. 195s F/GJO FIG. 9

FIG. 8

/N VEN TOR mbe/M @Ref WALTER PRAEG United States Patent O CURRENT SWITCHING DEVICE FDR ELECTRO- MAGNETIC HAMMERS Walter F. Praeg, Vancouver, British Columbia, Canada,

assiguor to Maxim Electronics Ltd., Vancouver, British Columbia, Canada, a corporation of British Co lumbia, Canada Application August 30, 1956, Serial No. 607,140

15 Claims. (Cl. S18-428) This invention relates to new and useful improvements in electromagnetic hammer design, operated by direct current whereby magnetic iields pull a movable magnetizable core back and forth. The invention assures maximum efficiency whether such a hammer is built for a few hundred watts or for several kilowatts and is herein illustratively described by reference to the preferred form thereof; however, it Will be recognized that certain modifications and changes therein with respect to details may be made without departing from the essential features involved.

Usually such hammers operate with two coils, one energized after the other. One coil pulls the movable core forward against the tool, after that the other coil pulls the movable core back preparing it for the next blow. Thus, for each cycle or hammer-blow one coil after the other has to be energized.

To transfer the direct current from one coil to the other two methods are known. In one, the ends of the two coils are brought to a switch separate from the hammer, and by means of this switch one coil after the other is energized. The other method uses a switch mechanism which is operated by the movable core mounted inside the hammer. Through the contacts of this switch mechanism one coil after the other is energized.

Both types of hammers have their advantages and disadvantages which will be apparent from the following description. As will be shown, my invention eliminates all their disadvantages but retains and improves their good features.

Figure 1 is an elevational section of a conventional hammer in which the direct current is switched from one coil to the other by an outside switch.

Figure 2 is a sectional view taken on line 2-2 of Figure l.

Figure 3 is an elevational section of a conventional hammer which switches the direct current from one coil to the other by means of a switch mechanism mounted inside the hammer, said switch being operated by the movable core.

Figures 4 through 8 show in principle how by means of my invention the direct current is transferred from one coil to the other.

Figure 7 represents an elevational section of a hammer according to the invention.

Figures 8 through l0 are sectional views taken on lines 8 8, 9-9 and 10-10, respectively, of Figure 7.

Referring to Figure 1 showing a conventional hammer, a movable core 108 is adapted to reciprocate longitudinally within a guide tube 106 and is connected to a tool 109 guided in a bearing 111 and positioned normally by a spring 112. Coils 104 and 105 wound or placed on 'non-magnetic square shaped tube 106 are received within the slots of E-shaped laminated ferromagnetic yokes 102 and 103. Coils 104 and 105 are connected through the main On-Olf switch 118, operable by a push button 119, to a direct current supply 121 and vibrating switch 122 in such manner that the current is switched irst to one coil and then to the other as long as the button 119 is pressed. Magnetic fields building up and collapsing alternately in opposite end portions of the core 108 drive the tool back and forth as desired.

Without pressing tool 109 against anything, merely spring 112 is deflected; with tool 109 pressed against solid matter, pay work is done. The rebound of core 103 from tool 109 varies in accordance with the degree of hardness and resilience of the work, as well as the force with which the tool is pressed against the material to be hammered. The switching frequency of switch 122 is constant, and because the rebound is variable, it may add to or subtract from the magnetic forces pulling core 108. Even with an electronic switch and minute manual adjustments so that 122 may switch from coil 104 to 105 shortly before, or at the moment of, or at a time after core 108 strikes tool 109, the rebound energy and the magnetic forces will drop out of step. For this reason a hammer operating on the described principle is ineiicient.

To overcome this drawback, hammers as illustrated in Figure 3 have been designed wherein the coil current transfer switch 322 is mounted inside the hammer and operated by the movable core 308 through a lever 323 or other actuating connection. The D.C. supply 321 is connected to the coils and switch 323 through a manually operated control switch 318 operable by a push button 319, as before.

With that prior art improvement substantially the correct relation between rebound and magnetic pull is achieved and is largely independent of the hardness and resilience of material being worked by tool 309. The hammer-blows per time unit will change only with various static pressures exerted on the hammer, and With the diiferent hardnesses of the materials being hammered. The hammer would never fall out of step with the switching rate.

However, even an improved prior art hammer such as that shown in Figure 3 is subject to the following shortcomings (A) A portion of the magnetic force moving core 308 must be used to operate switch 322.

(B) The contacts of switch 322 must handle the full coil current. With the high switching rate involved, and due to the fact that direct current owing through an inductance has to be interrupted, a relative expensive switch must be used.

(C) Regular maintenance and contact-care is necessary to keep switch 322 operative.

(D) The bulk of housed switch 322 to the bulkiness of the hammer.

The present invention, representing an improvement in the type of switch depicted generally in Figure 3, overcomes the aforementioned shortcomings by using small mechanical timing switches inside the hammer, and electronic coil-switching devices externally of the hammer which carry the heavy coil current but are controlled by the small internal timing switches.

The schematic diagrams of Figures 4, 5 and 6 show in principle the different phases of operation of this improvement. ln Figure 4 numerals 401 and 402 denote normally open switch contacts mounted inside the hammer. A switch-actuating rod 4103 is permanently fastened to the hammer core and carries a tab or disk tilllpositioned to close switches 01 and 402 alternately as the rod reciprocates. Hammer coils 404 and 405 are respectively connected between D.C. source 408 and the anodes of gas lled tubes 406 and 407, for instance thyratrons. A direct current bias supply .110 for tubes 406 and 407 is connected between their grids and commonly connected cathodes through the respective resistors 411 and 412 in adds objectionably order to maintain these tubes normally non-conductive.'

The negative terminal of a direct current trigger bias supply 413 is connected to the negative side of source 410, While the positive terminal of supply 413 is connected to the interconnection between corresponding contacts of switches 401 and 402. The remaining contact of switch 401 is connected to the control grid of tube 406, while that of switch 402 is connected to the control grid of tube 407.

In the operation of this system let it be assumed that tab 414 momentarily closes contacts 401 as shown in Fig ure 4. Thyratron 406 tires because during closure of contacts 401 the Voltage of supply 413 is impressed upon resistor 411 with such a polarity that the bias voltage between control grid and cathode of 406 is overcome sufficiently to trigger the gas tube. With tube 406 conducting, current ows from the positive side oi source 408 through the hammer coil 404 and thyratron 406 back to the negative side of source 408 as indicated by the solid pointers. The magnetic field that builds up around coil 404 pulls the core back, thus moving tab 414 away from switch 401 towards switch 402. Switch 401 opens, but since tube 406 is a gas-vapor tube it remains ionized. However, with the small voltage drop across tube 406 in relation to the total voltage of source 408, capacitor 409 is charged nearly to the full voltage of the latter through a circuit including coil 405, condenser 409, tube 406 and the source 408, as indicated by the dotted pointers. As shown in Figure 5, when tab 414 now closes switch 402, triggering 407, both tubes 406 and 407 are momentarily conductive. When tube 407 becomes conductive, its anode potential drops. Since this sudden reduction of potential is transmitted through charged capacitor 409, the anode potential of tube 406 also drops correspondingly and thereby becomes insufficient to sustain conduction in the latter tube. The tube 406 is permitted to become extinguished at that instant despite sel-inductance in coil 404, because the energy stored in this coil is permittcd to flow into and through condenser 409 in a circuit including such condenser, the now conductive tube 407 and source 408. Once tube 406 is extinguished, it cannot tire again until retriggered by closure of switch 401, because of the bias voltage supplied by source 408. With tube 407 conductive current ilows now through hammer coil 405 only, and the condenser 409 becomes recharged, but with reverse polarity, as shown in Figure 6. The magnetic iield around coil 405 pulls the core against the tool, and rod 403, attached to the core, follows this motion. When tab 414 reaches contacts 401 tube 406 will again be tired and tube 407 will be extinguished. Self inductance of coil 405 causes discharge of condenser 409 through tube 406, thus dropping the plate voltage of tube 407 to the point where it ceases to conduct, the reverse of the role of this condenser with respect to the tubes when tube 406 is to be extinguished.

Circuits as comprised basically by capacitor 409, tubes 406 and 407, and a ioad represented by coils 404 and 405 have been described as early as 1940 and serve with the shown modifications as an excellent switching device for this application.

The main feature of my invention is to control such a switching device by means of two simple, small switches mounted inside the hammer and acting via bias supply 413. In case very large coil currents have to be handled and ignitrons are used as tubes 406 and 407, an interposing stage between switches 401 and 402 and the ignitron igniters should be used whereby the momentary closure of switch 401 or switch 403 initiates suitable ign nitron trigger pulses. Suitable intermediate stages are well known in the art and need no present discussion. The hammer current circuit would in principle still appear as in Figures 4 through 6.

Figure 7 shows a hammer according to my invention. Casing 701 encloses laminated ferromagnetic yoke bodies 702 and 703 shaped like an E. Laminated ferromagnetic bodies 704 and 705 are placed between the ends of the .4 two E-shaped yokes 702 and 703 in order to minimize the magnetic reluctance of the yoke assembly cooperating with reciprocative core 715. End pieces 704 and 705 are also used to center the nonmagnetizable tube 708 of substantially square cross section on which coils 706 and 707 are Wound. The tube 708 has end flanges 709 completing the coil form or spool. Tool 710 has an enlargement 711 with a groove to accommodate spring 712 which is fastened to housing 701. Bearing 713 is pressed into end piece 704 to guide tool 710. Bearing 714 is pressed into end piece 705 to guide rod 717. The latter in turn is pressed into core 715 which is made from solid or laminated ferromagnetic material. The ends of end pieces 704 and 705 facing core 715 are bevel'led or chamfered and the ends of such core are complementally recessed to make the effective length of the lines of magnetic force traversing the air gaps therebetween shorter than the actual linear distance of opposing points measured parallel to the axis, thus decreasing the magnetic reluctance. A hardened steel piece 716 having a rounded end face is pressed into core 715 that will stand up to the impact of the core upon tool 710.

A rod 717 is threaded into the opposite end of core 715, and a switch control tab 724 in the form of a disk ot insulating material is mounted by the nuts 725 on the projecting end of this rod. Housing 701 includes a main On-Oft switch 722 adapted to be operated by a push button 723. Small and compact timing switches 726 and 727 are mounted on a support 735 within housing 701 and are connected to control the operation of externally situated electronic switch mechanism handling the ilow of currents in coils 706 and 707. The effective distance between switches 726 and 727 can be adjusted by turning an adjusting screw 730 having a head 731 which carries a set screw 732. The ends of screw 731 are journalled in bearings 733 and 734 located in housing 701. The threaded portions of the screw on either side of its midlocation, which engage the switches, have threads of opposite hand so that turning of the screw effects the required change of spacing between switches.

One end 718 of hammer coil 706 is connected to the anode of a thyratron 737, while one end 721 of hammer coil 707 is connected to the anode of thyratron 738. The opposite ends 719 and 720 of the respective coils 706 and 707 are connected together and terminate on one contact of switch 722. The other contact of switch 722 is connected to the positive pole of direct current supply 744. The negative pole of supply 744 terminates on the cathodes of tubes 737 and 738. A bias supply 742 for tubes 737 and 738 has its negative pole connected to the grids of; these tubes through resistors 740 and 741, and its positive pole connected to the cathodes of these tubes. The negative pole of direct current Supply 739 is connected to the negative side of bias supply 742. The positive side of supply 739 terminates on corresponding mutually adjacent contacts of switches 726 and 727. The remaining or outer contact of switch 726 is connected to the grid of tube 738, and that of switch 727 is connected to the grid of tube 737. A normally open switch 728 is connected in parallel to either contact pair 726 or 727 and has a push button 729 which may be pressed in order to trigger one tube when core 715 is in such a position that neither of switches 726 nor 727 is closed. This initiates operation of the' hammer. Such operation continues as long as switch 722 remains closed. As will be evident, during such operation coils 706 and 707 will be energized one after the other governed by the switches 726 and 727, actuated in proper timing by the movements of disk 724. Blowout condenser 743 enables this as described in Figures 4 through 6.

The number of hammer blows per time unit depends on the distance between the control switches, the magnetic pulls exerted upon core 715, the combined mass of elements 715, 717, 724 and 725, and the rebound ,Y

energies upon core 715 when the latter strikes tool 710 or spring 736 which is interposed between the core and end piece 705.

Preferably the electronic switch is housed together With direct current supply 744 in one cabinet 745; however, they might be separated, for instance, if supply 744 consists of an engine-driven direct-current generator.

Figures 8 through 1,0 show dilferent cross sections of Figure 7 in order to give a clearer understanding. 'Ihe numeral 746 indicates mounting hardware used to fasten the various hammer parts to each other and the housing, and 747 denotes mounting holes.

As previously described the distance between control switches 726 and 727 and the relative position of disk 724 are adjustable. This permits adjusting the number of hammer blows per time unit. If switches 726 and 727 are closer together, the number of hammer blows per time unit will increase; however, the hammer energy per blow will be decreased; if switches 726 and 727 are spaced farther apart, the number of hammer blows per time unit will decrease and the hammer energy per blow will increase.

Since switch 726 must be closed at such a time that the maximum rebound of core 715 from tool 710 adds to the magnetic pull of coil 707, such closure should be erected when both core 715 and tool 710 are in a specific position in relation to each other. The relative positions of elements 715 and 710, for maximum eiciency, are practically independent of the number of hammer blows per time unit; therefore, control switch 726 and disk 724 could be non-adjustably mounted if desired, leaving only control switch 727 adjustable to change the number of hammer blows per time unit by varying the distance between switches 726 and 727. Spring 736 compensates automatically for the shorter distance travelled by core 715; spring 736 could be made adjustable as well.

These adjustments being made once, for a certain average switching rate per time unit, the number of hammer blows per time unit will vary around this average rate depending on whether hard or soft material is being worked by tool 710. Since core 715 operates the tool indirectly, the rebound energies and the magnetic pulls will always add to each other and never slip out of step.

In any arrangement of the control switches, with both, or only one, adjustable, these comparatively small and inexpensive switches control, by their relatively small currents, the transfer of relatively heavy hammer coil currents. Hence these switches are not exposed to wear (oscillators, shapers, amplifiers, etc.). The sanne type fdue to this current and the relatively heavy power supply voltage. No complicated trigger circuits are required of switches (726 and 727) and switch operation devices (717, 724, 725, 730, 731, 732, 733, 734 and 735) can be used for a great variety of hammers ranging in power consumption from a few hundred watts to several kilowatts. With ignitrons as power tubes, switches 726 and 727 trigger a simple interposing stage which in turn controls the ignitrons.

The simplicity of the circuit eliminates maintenance for the coil current circuit to the point Where only faulty tubes have to be exchanged; the control circuit switches need practically no maintenance at all.

It is obvious that changes can be made in the form, construction and arrangement of the control switches, as shown within the scope of the appended claims, without departing from the spirit of my invention, and I Ado not, therefore, Wish to limit myself to the exact construction and arrangement shown and described herein.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. Electromagnetic vibrator tool means comprising in combination with a tool body, a tool armature having a ferromagnetic core guided for reciprocation in said tool body, and two spaced electromagnet coils, one a driving coiland the other a retraction coil, mounted in said tool body in relation to each other and to said armature core to draw the latter magnetically back and forth on a driving stroke and on a rebound-retraction stroke, respectively, by alternate energization of the respective coils; two control switch means mounted in said tool body, said armature further comprising switch actuator means operated by movement of said core, and said `two switch means having, respectively, spaced operating elements positionally related to said switch actuator means for alternate actuation thereby, one such switch means comprising a retraction stroke control switch and being arranged for actuation by the driving stroke of said armature core, and the other such switch means comprising a driving stroke control switch and being arranged for actuation -by the rebound-retraction stroke of said core, an external Voltage source adapted for supplying energizing `current to said coils, two switch devices having main current carrying means, each such main current carrying means being connected in circuit respectively with a different one of said coils and with said voltage source, ,said switch devices further having electrically lsensitive control means operable by switch actuation for interrupting and restoring conductivity through the respective Switch devices, the control means of the switch device connected to the driving coil being connected to the driving stroke control switch means to be rendered conductive by actuation of such control switch means, the control means of the switch device connected to the retraction coil being connected to the retraction stroke control switch means to be rendered conductive by actuation of such latter control switch means, each such Switch device being adapted to remain nonconductive until rendered conductive by its control means, and means operable for extinguishing conduction in said switch devices individually, said latter means being connected to each such switch device and operated by the rendering of the other switch device conductive, Whereby one coil is deenergized while the other is energized.

2. Electromagnetic vibrator tool means comprising in combination with a tool body, a tool armature having a ferromagnetic core guided for reciprocation in said tool body, and two spaced electromagnet coils, one a driving coil and the other a retraction coil, mounted in said tool body in relation to each other and to said armature core to draw the latter magnetically back and forth on a driving stroke and on a rebound-retraction stroke, respectively, by alternate energization of the respective coils; two control switch means mounted in said tool body, said armature further comprising switch actuator means operated by movement of said core, and said two switch means having, respectively, spaced operating ele- :ients positionally related to said switch actuator means for alternate actuation thereby, one such switch means comprising a retraction stroke control switch and being arranged for momentary actuation by the driving stroke of said armature core, and the other such switch means comprising a driving stroke control switch and being arranged for momentary actuation by the rebound-retraction stroke of said core, an external voltage source adapted for supplying energizing current to said coils, two switch devices having main current carrying means, each `such main current carrying means being connected in circuit respectively with a different one of said coils and with said voltage source, said switch devices further having electrically sensitive control means operable by switch actuation for interrupting and restor` ing conductivity through the respective switch devices, the control means of the switch device connected to the driving coil being connected to the driving stroke control switch means to be rendered conductive by actuation of such control switch means, the control means of the switch device connected to the retraction coil being connected to the retraction Istroke control switch means yto be rendered conductive by actuation of such latter control switch means, each such switch device being adapted to remain nonconductive until rendered conductive by its control means, and each switch device, once conductive, being adapted to remain conductive, until extinguished from without, for continuing the energization of the associated coil, and means operable for extinguishing conduction in said switch devices individually, said latter means being connected to each such switch device and operated by the rendering of the other switch device conductive, whereby one coil is deenergized While the other is energized.

3. The vibrator tool means defined in claim 2, wherein the conduction extinguishing means comprises means forming current paths connected to the respective coils for discharging the selfainductance energy from either such coil upon energization of the other coil.

4. The vibrator tool means defined in claim 3, wherein the switch devices comprise gaseous discharge means having an anode and cathode as their main current carrying means, the anodes being connected to corresponding ends ot the two coils, and wherein the conduction extinguishing means comprises capacitance means connected between anodes of the gaseous discharge devices.

5. The vibrator tool means defined in claim 4, wherein the switch actuator means and the respective spaced operating elements for the two switch means are positionally adjustable in relation to each other, thereby permitting adjustment of the frequency of reciprocation of the armature core and separate adjustment of the tool for securing maximum eiciency therefrom by timing energization of the retraction coil in relation to the rebound of the armature.

6. The vibrator tool means defined in claim 4, wherein the operating element of the driving control switch and the switch actuator means are relatively adjustable in position, whereby the frequency of reciprocation of the armature core may be adjusted without materially changing the relative timing of energization of the retraction coil and rebound of the armature.

7. The vibrator tool means defined in claim 4, wherein the driving control switch means operating element is adjustably mounted in the tool body for changing the relative spacing between the two operating elements to vary the frequency of vibration and to vary the timing of energization of the driving coil in relation to retraction of the armature.

8. The vibrator tool means defined in claim 4, wherein the tool additionally comprises starter switch means having contacts arranged for initiating energization of one of the coils independently of the position of the armature core, said starter switch means comprising a manual actuating element adapted for momentary actuation.

9. The vibrator tool means defined in claim 2, wherein the tool additionally comprises starter switch means having contacts arranged for initiating energization of one of the coils independently of the position of the armature core, said starter switch means comprising a manual actuating element adapted for momentary actuation.

10. T he vibrator tool means defined in claim 2, wherein the switch actuator means and the respective spaced operating elements for the two switch means are positionally adjustable in relation to each other, thereby permitting adjustment of the frequency of reciprocation of the armature core and separate adjustment of the tool for securing maximum efficiency therefrom by tim* ing energization of the retraction coil in relation to the rebound of the armature.

1l. The vibrator tool means defined in claim 2, wherein the driving control switch means operating element is adjustably mounted in the tool body for changing the relative spacing between the two operating elements to 8 vary the frequency of vibration and to vary the timing of energization of the driving coil in relation to retraction of the armature. v f

l2. Electromagnetic vibrator tool means comprising in combination with a tool body, -a tool armature having a ferromagnetic core guided for reciprocation in'said tool body, and two spaced electromagnet coils, one a driving coil and the other a retraction coil, mounted in said tool body in relation to each other and to said armature core to draw the latter magnetically back and forth on a driving stroke and on a rebound-retraction stroke, respectively, by alternate energization of the respective coils; two control switch means mounted in said tool body, said armature further comprising switch actutaor means operated by movement of said core, and said two switch means having, respectively, spaced operating elements positionally related to said switch actuator means for alternate actuation thereby, one such switch means comprising a retraction stroke control switch and being arranged for momentary actuation by the driving stroke of said armature core, and the other such switch means comprising a driving stroke control switch and being arranged for momentary actuation by the rebound-retraction stroke ofv said core, an external voltage source adapted for supplying energizing current to said coils, two gaseous discharge devices having a set of main current carrying electrodes, each such set being connected to form an eneregizing circuit, including said voltage source, for a different one of said coils, said source having a terminal connected to one end of each coil, said gaseous discharge devices also having a biascontrolled starter electrode adapted, by application of starting voltage thereto, to initiate. conduction in said devices, respectively, starting voltage supply means, circuit means including said retraction control switch means and said starting voltage supply means connected for applying starting voltage to the starter electrode of the gaseous discharge device connected to the retraction coil, by actuation of said retraction control switch means, circuit means including said driving control switch means and said starting voltage supply means connected for applying starting voltage to the starter electrode of the other gaseous discharge device, by actuation of the driving control switch means, and capacitance means having opposite terminals connected to the ends 0f the two coils opposite the ends thereof connected to said source terminal and adapted to extinguish conduction in either such gaseous discharge device when the other is rendered conductive and to provide a path for discharge of self-inductance energy stored in the coil energized through the extinguished device.

13. The vibrator tool defined in claim 12, wherein at least the operating element of the driving control switch means is adjustably mounted in the tool body for positional adjustment in relation to the other switch means operating element.

14. The Vvibrator tool defined in claim 13, wherein the switch actuator means is positionally adjustable in relation to the armature core in a sense causing adjustment of the timing of actuation of the control switch means in relation to movement of the armature. j

15. The vibrator tool means defined in claim 12, and manually operable switch means connected to the starting voltage source and arranged for applying starting voltage to the starting electrode of one of the gaseous discharge devices by operation of said latter switch means, thereby to start operation of the tool in case the armature occupies an intermediate position wherein neither control switch means is actuated.

References Cited in the le of this patent` UNITED STATES PATENTS 2,285,434 Hittson Ilmey 9, 1942 

